D-Link DFL-260E User Manual for DFL-260E - Page 183
Policy-based Routing, group, provider-independent metropolitan area networks, Routing Tables
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4.3. Policy-based Routing Chapter 4. Routing 4.3. Policy-based Routing Overview Policy-based Routing (PBR) is an extension to the standard routing described previously. It offers administrators significant flexibility in implementing routing decision policies by being able to use different routing tables according to specified criteria. Normal routing forwards packets according to destination IP address information derived from static routes or from a dynamic routing protocol. For example, using OSPF, the route chosen for packets will be the least-cost (shortest) path derived from an SPF calculation. Policy-based routing means that routes chosen for traffic can be based on specific traffic parameters. Policy-based routing allows the following to be possible: • Source-based Routing A different routing table may need to be chosen based on the source of traffic. When more than one ISP is used to provide Internet services, policy-based routing can route traffic originating from different sets of users through different routes. For example, traffic from one address range might be routed through one ISP, whilst traffic from another address range might be through a second ISP. • Service-based Routing A different routing table might need to be chosen based on the service. Policy-based routing can route a given protocol such as HTTP, through proxies such as Web caches. Specific services might also be routed to a specific ISP so that one ISP handles all HTTP traffic. • User-based Routing A different routing table might need to be chosen based on the user identity or the group to which the user belongs. This is particularly useful in provider-independent metropolitan area networks where all users share a common active backbone but each can use different ISPs and subscribe to different providers. PBR Components Policy-based routing implementation in NetDefendOS is implemented using two components: • Additional Routing Tables One or more user-defined alternate Routing Tables are created in addition to the standard default main routing table. • Routing Rules One or more Routing Rules are created to determine which routing table to use for which traffic. Without routing rules, the main routing table is the default. Routing Tables 183